1. Field of the Invention
The present invention relates to an active matrix light emitting device, and in particular, relates to a structure of a portion through which light is emitted.
2. Description of the Related Art
A light emitting device utilizing light emitted by an electroluminescent element (a light emitting element) has been attracting attention as a display device with a wide viewing angle and low power consumption.
Light emitting devices that are mainly used for displaying images are classified into an active matrix light emitting device and a passive matrix light emitting device. An active matrix light emitting device can control lighting, non-lighting and the like of light emitting elements for each light emitting element. Therefore, the active matrix light emitting device can be driven at lower power consumption than a passive matrix light emitting device, and hence, the active matrix display device is suitable to be mounted not only on a small electric appliance (e.g., a cellular phone) as its display portion but also on a large size television receiver or the like as its display portion.
In addition, with respect to an active matrix light emitting device, a circuit for driving a light emitting element is provided for each light emitting element. The circuits and the light emitting elements are arranged over a substrate such that light emitted from the light emitting elements to the outside is not hindered by the circuits. Also, a plurality of insulating layers with light transmitting properties are laminated in portions overlapping with the light emitting elements and light is emitted to the outside through these insulating layers. These insulating layers are provided to form a transistor, which is a constituent element of the circuit, a circuit element such as a capacitor element, or a wiring.
When light passes through the laminated insulating layers, multiple interference of light is sometimes caused due to difference in refractive index of the respective insulating layers. This causes problems in which the emission spectrum is changed depending on an angle for seeing a surface through which light is emitted, and the visibility of an image displayed on the light emitting device is deteriorated.
Also, the deterioration in visibility of an image, which is caused due to the variation in refractive index for each layer, is also caused in a passive matrix light emitting device. For example, the patent document 1 raises a problem in which the visibility is deteriorated by reflecting outside light and light emitted from a light emitting element at an interface due to the variation in refractive index of respective layers constituting the light emitting element. The patent document 1 proposes a light emitting element with an improved element structure so as to overcome this problem.
[Patent Document 1] Japanese Patent Application Laid-Open No. Hei 7-211458